The present invention relates to methods and devices for treatment of saline-alkali land, and in particular, methods and devices for treating saline-alkali land by a self-circulating process, without addition of chemicals or introduction of fresh water.
Salts in soil are essential nutrients for growth of crops, but growth of crops may be inhibited by salt stress when the salt content in soil exceeds 0.1%. A land where the salt content in the soil exceeds 0.1% and thus plant growth is inhibited is generally called saline-alkali land. Saline-alkali lands can be classified into mild saline-alkali land, medium saline-alkali land, and severe saline-alkali land. In general, the salt content in soil of mild saline-alkali land ranges from 0.1% to 0.3%, the salt content in soil of medium saline-alkali land ranges from 0.3% to 0.6%, and the salt content in soil of severe saline-alkali land is >0.6%.
Currently, methods for treatment of saline-alkali land mainly include physical amelioration, chemical amelioration, biological amelioration, and water amelioration. These methods share the same problem that they do not extract salts from soil but merely change the rule of salt migration. Therefore, these methods may have poor treatment effect, require repeated treatments, long treatment periods, and large investment, and consume a large amount of water resource. Pat. Pub. No. CN1236537A discloses a method for physically ameliorating saline-alkali land, in which the salt content of saline-alkali land is reduced by deep ploughing, irrigating and draining, and leaching with fresh water. The method is simple in operation, but has poor ameliorating effect and the problem of repeated increase of salt content. Pat. Pub. No. CN101134898A discloses a method for chemically ameliorating saline-alkali land, in which salts are isolated by a saline-alkali land improver to protect the root system of crops. Although the method can increase the survival rate of crops, the improver comprises complicated components and thus has a large influence on the ecological environment, and the method is costly because of the need of continuous investment. Pat. Pub. Nos. CN1559709A and No. CN192645A disclose a method for biologically ameliorating saline-alkali land, in which the salt content in soil is decreased by growing salt-tolerant plants that absorb salts. However, the salt-tolerant plants need long breeding periods and have poor regional adaptability. Pat. Pub. Nos. CN1765169A and CN1799301A disclose a method for ameliorating saline-alkali land by water conservancy, in which salt content in solid is decreased with concealed conduits or salt removing tanks as means for water conservancy. The method is costly and needs maintenance all the year round. All the above four amelioration methods are based on consumption of a large amount of fresh water. The water resources in the region where saline-alkali land is treated may comprise all saline-alkali water, and hence it may require introducing fresh water from other regions, thereby intensifying the contradiction of freshwater resource allocation in the country.
In addition, Pat. Pub. Nos. CN10189804A, CN2740595Y, and CN1073664A disclose a method for decreasing salt content in saline-alkali water with a centrifuge or an electronic treatment apparatus. By the method, salts in saline-alkali water can be extracted in a short time. However, very strict technical conditions must be satisfied when saline-alkali land is treated with these complicated and precise apparatus. As a result, desalination of saline-alkali water is costly, and it is difficult to realize large-scale treatments of saline-alkali land with a low cost. Moreover, the desalting apparatus need to be powered by supply of conventional electricity or motive force electricity, and thus the method is difficult to be applied to saline-alkali lands that are distributed broadly and scattered loosely.